In several forms of bladder injury, loss of epithelial barrier function is associated with failure of normal filling and emptying function, so that frequency, urgency/incontinence, and pain occur. Millions of people suffer these symptoms each year, ranging in duration from brief episodes in young women with bacterial cystitis, to chronic symptomatology of waxing and waning severity in patients with interstitial cystitis, to chronic severe dysfunction in patients suffering the effects of radiation cystitis and hemorrhagic cystitis due to cyclophosphamide therapy. At present, almost nothing is known about the mechanisms of bladder epithelial damage and the effects of failure of the bladder permeability barrier on the underlying muscle and nerves. The proposed experiments will examine the mechanisms of bladder epithelial damage in two models of cystitis and will determine how acute loss of epithelial barrier integrity affects the function of bladder muscle and afferent nerves. In the first funding period, we provided the first quantitative analysis of the permeability properties of the bladder permeability barrier and developed a preliminary understanding of the trafficking mechanisms responsible for changing the surface area of the apical membrane in response to bladder filling and emptying. In addition, they developed from reconstituted bilayers a model of how the apical membrane is structured to function as a barrier. Using models of barrier injury derived directly from the first funding period, this competing renewal application has three specific aims. In Aim #1, rabbit bladder epithelium will be subjected to ischemic injury in the Ussing chamber. Initial studies will define the ability of the epithelium to recover from the injury. Next, the effects of ischemia on the determinants of barrier function (the tight junctions, the apical membrane and the mechanisms for trafficking of membrane into and out of the apical surface) as well as other cell structures and activities critical to barrier function (energy generation and the cytoskeleton) will be defined. In Aim #2, bladders of guinea pigs sensitized to ovalbumin will be exposed to apical ovalbumin, leading to inflammation of the bladder wall. Initial studies will define in detail the time course of loss of barrier function and its recovery in this model. Subsequent studies will define the effects of bladder inflammation on the determinants of barrier function and their supporting structures and activities, as well as the role of specific mediators in epithelial injury. In Aim #3, the permeability barriers of rat bladders will be disrupted in situ with protamine sulfate and the effects of the resulting leakage of urinary constituents on the function of the underlying bladder muscle and the activity of bladder afferents will be determined. The proposed studies will provide the first mechanistic examination of the failure of the bladder permeability barrier in ischemic and inflammatory injury, and will determine directly whether leakage of urinary constituents per se leads to dysfunction of the underlying musculature and increase in afferent nerve traffic.